The term deontological was first used to describe the current, specialised definition by C. D. Broad in his book, Five Types of Ethical Theory, which was published in 1930.[5] Older usage of the term goes back to Jeremy Bentham, who coined it before 1816 as a synonym of Dicastic or Censorial Ethics (i.e. ethics based on judgement).[6]
The more general sense of the word is retained in French, especially in the term code de déontologie (ethical code), in the context of professional ethics.

Depending on the system of deontological ethics under consideration, a moral obligation may arise from an external or internal source, such as a set of rules inherent to the universe (ethical naturalism), religious law, or a set of personal or cultural values (any of which may be in conflict with personal desires).

Immanuel Kant's theory of ethics is considered deontological for several different reasons.[7][8] First, Kant argues that to act in the morally right way, people must act from duty (Pflicht).[9] Second, Kant argued that it was not the consequences of actions that make them right or wrong but the motives of the person who carries out the action.

Kant's argument that to act in the morally right way one must act purely from duty begins with an argument that the highest good must be both good in itself and good without qualification.[10] Something is "good in itself" when it is intrinsically good, and "good without qualification", when the addition of that thing never makes a situation ethically worse. Kant then argues that those things that are usually thought to be good, such as intelligence, perseverance and pleasure, fail to be either intrinsically good or good without qualification. Pleasure, for example, appears not to be good without qualification, because when people take pleasure in watching someone suffer, this seems to make the situation ethically worse. He concludes that there is only one thing that is truly good:

Nothing in the world—indeed nothing even beyond the world—can possibly be conceived which could be called good without qualification except a good will.[10]

Kant then argues that the consequences of an act of willing cannot be used to determine that the person has a good will; good consequences could arise by accident from an action that was motivated by a desire to cause harm to an innocent person, and bad consequences could arise from an action that was well-motivated. Instead, he claims, a person has a good will when he 'acts out of respect for the moral law'.[10] People 'act out of respect for the moral law' when they act in some way because they have a duty to do so. So, the only thing that is truly good in itself is a good will, and a good will is only good when the willer chooses to do something because it is that person's duty, i.e. out of "respect" for the law. He defines respect as "the concept of a worth which thwarts my self-love".[11]

Act only according to that maxim by which you can also will that it would become a universal law.

Act in such a way that you always treat humanity, whether in your own person or in the person of any other, never simply as a means, but always at the same time as an end.

Every rational being must so act as if he were through his maxim always a legislating member in a universal kingdom of ends.

Kant argued that the only absolutely good thing is a good will, and so the single determining factor of whether an action is morally right is the will, or motive of the person doing it. If they are acting on a bad maxim, e.g. "I will lie", then their action is wrong, even if some good consequences come of it.
In his essay, On a Supposed Right to Lie Because of Philanthropic Concerns, arguing against the position of
Benjamin Constant, Des réactions politiques, Kant states that "Hence a lie defined merely as an intentionally untruthful declaration to another man does not require the additional condition that it must do harm to another, as jurists require in their definition (mendacium est falsiloquium in praeiudicium alterius). For a lie always harms another; if not some human being, then it nevertheless does harm to humanity in general, inasmuch as it vitiates the very source of right [Rechtsquelle] ... All practical principles of right must contain rigorous truth ... This is because such exceptions would destroy the universality on account of which alone they bear the name of principles."[12]

Although not all deontologists are religious, some believe in the 'divine command theory', which is actually a cluster of related theories which essentially state that an action is right if God has decreed that it is right.[13] According to Ralph Cudworth, an English philosopher, William of Ockham, René Descartes, and eighteenth-century Calvinists all accepted various versions of this moral theory, as they all held that moral obligations arise from God's commands.[14] The Divine Command Theory is a form of deontology because, according to it, the rightness of any action depends upon that action being performed because it is a duty, not because of any good consequences arising from that action. If God commands people not to work on Sabbath, then people act rightly if they do not work on Sabbath because God has commanded that they do not do so. If they do not work on Sabbath because they are lazy, then their action is not truly speaking "right", even though the actual physical action performed is the same. If God commands not to covet a neighbour's goods, this theory holds that it would be immoral to do so, even if coveting provides the beneficial outcome of a drive to succeed or do well.

One thing that clearly distinguishes Kantian deontologism from divine command deontology is that Kantianism maintains that man, as a rational being, makes the moral law universal, whereas divine command maintains that God makes the moral law universal.

Bocheński (1965) makes a distinction between deontic and epistemic authority.[15]
A typical example of epistemic authority in Bocheński's usage would be "the relation of a teacher to his students" or "the relation between an employer and his employee".[16] A teacher has epistemic authority when making declarative sentences that the student presumes is reliable knowledge and appropriate but feels no obligation to accept or obey; in contrast, an employer has deontic authority in the act of issuing an order that the employee is obliged to accept and obey regardless of its reliability or appropriateness.[16]

Frances Kamm's "Principle of Permissible Harm" (1996) is an effort to derive a deontological constraint which coheres with our considered case judgments while also relying heavily on Kant's categorical imperative.[17] The Principle states that one may harm in order to save more if and only if the harm is an effect or an aspect of the greater good itself. This principle is meant to address what Kamm feels are most people's considered case judgments, many of which involve deontological intuitions.
For instance, Kamm argues that we believe it would be impermissible to kill one person to harvest his organs in order to save the lives of five others. Yet, we think it is morally permissible to divert a runaway trolley that would otherwise kill five innocent and immobile people onto a side track where one innocent and person will be killed.
Kamm believes the Principle of Permissible Harm explains the moral difference between these and other cases, and more importantly expresses a constraint telling us exactly when we may not act to bring about good ends—such as in the organ harvesting case.
In 2007, Kamm published a book that presents new theory that incorporates aspects of her "Principle of Permissible Harm", the "Doctrine of Productive Purity".[18] Like the "Principle of Permissible Harm", the "Doctrine of Productive Purity" is an attempt to provide a deontological prescription for determining the circumstances in which people are permitted to act in a way that harms others.

^Jeremy Bentham, Chrestomathia (1816), p. 213:
"For a synonym, Dicastic Ethics may have the single-worded appellative Deontology. [Deontology.] From two Greek words, the first of which signifies fit, fitting, right, becoming, proper. Deontology—an account or indication of that which, on the occasion in question, whatsoever it be, is—(i.e. by him who speaks or writes, is regarded as being)—fit, fitting, becoming, proper. It is in sound only, and not in signification, that it has any connexion with the word ontology, employed above. Applied to every branch of Ethics, taken in the largest sense of the word Ethics, the use of such a word as Deontology affords a promise of being attended with considerable convenience. It will accord equally well with every system which ever has been, or ever can be, devised, in relation to the foundation of moral obligation :—in the use of it, no such incongruity and presumption is involved, as that which is called petitio principii—i.e. a begging of the question—an assumption of the matter in dispute."
Also explained as "the knowledge of what is right and proper":
"Deontology is derived from the Greek words, το δεον (that which is proper) and Λογια, knowledge — meaning the knowledge of what is right and proper; and it is here specially applied to the subject of morals, or that part of the field of action which is not the object of public legislation. As an art, it is the doing what is fit to be done; as a science, the knowing what is fit to be done on every occasion."
Deontology or, The science of morality : in which the harmony and co-incidence of duty and self-interest, virtue and felicity, prudence and benevolence, are explained and exemplified : from the MSS. of Jeremy Bentham ed. Bowring (1834), p. 21.

^Vardy, Charlotte (April 2012). Ethics Matters. SCM Press. ISBN978-0-334-04391-1. Retrieved 19 August 2013. In How to Make Good Decisions and Be Right All the Time: Solving the Riddle of Right and Wrong, London: Continuum 2008, Iain King develops a quasi-utilitarian system compatible with consequence-, virtue- and act based ethics.